The present invention relates to an electron beam irradiation device and method and, more specifically, to an electron beam irradiation device and an electron beam irradiation method which are utilized for removing harmful constituents contained in exhaust gas discharged from, for example, a steam power station.
It is considered that greenhouse effect, acid rain and other effects due to air pollution, which have become the problems throughout the world, originate from constituents such as SOx, NOx, etc., which are included in combustion exhaust gas exhausted from, for example, a thermal power station, etc. One method, which is practiced, for removing harmful constituents such as SOx, NOx, etc., is to irradiate an electron beam on the combustion exhaust gas, thereby carrying out desulfurization and denitration (removal of harmful constituents such as SOx, NOx, etc.).
FIG. 1 shows an example of an electron beam generation device which is used for the above application. The combustion exhaust gas processing device mainly comprises: a power supply 10 which generates a high DC voltage; an electron beam irradiation device 11 which irradiates an electron beam on the combustion exhaust gas; and a flow path 19 for the combustion exhaust gas which is placed along an irradiation window 15 which is an exit for the electron beam irradiated by the device 11. The electron beam, which is emitted from the irradiation window 15 to the outside, irradiates molecules of oxygen (O.sub.2), steam (H.sub.2 O), etc., in the combustion exhaust gas, wherein the irradiation window 15 comprises, for example, a thin film of titanium, etc. By receiving the irradiation, these molecules become free radicals such as OH, O, HO.sub.2, etc., which have very strong oxidative power. These free radicals oxidize harmful constituents such as SOx, NOx, etc., and form intermediate products such as sulfuric acid, nitric acid, etc. These intermediate products chemically react with ammonia gas (NH.sub.3) which is injected in advance, and become ammonium sulfate and ammonium nitrate. The ammonium sulfate and ammonium nitrate are recovered as materials for fertilizer. By using such an exhaust gas processing system, it becomes possible to remove harmful constituents such as SOx, NOx, etc., from the combustion exhaust gas, and recover byproducts such as ammonium sulfate and ammonium nitrate which can be used as materials of fertilizer.
The electron beam generation device 11 mainly comprises: a thermoelectron generation source 12 such as a thermoelectron filament, etc.; an accelerating tube 13 for accelerating electrons emitted from the thermoelectron generation source 12; a focusing electromagnet 16 for applying a magnetic field to a high energy electron beam formed by the accelerating tube, thereby controlling the beam diameter of the electron beam; and a scanning electromagnet 17 for applying a magnetic field to the electron beam, of which beam diameter is controlled, thereby deflecting the electron beam. These elements are contained within enclosing elements 18a and 18b and are held in a high vacuum atmosphere. The thus formed high energy electron beam is deflected and scanned by the magnetic field applied by the scanning electromagnet 17, and emitted from the irradiation window 15 to a predetermined area of the flow path 19 of the exhaust gas.
FIG. 2(a) is a drawing which shows deflecting and converging of a beam which is formed by a conventional focusing electromagnet and a scanning electromagnet. For example, thermoelectrons generated by a thermoelectron generation source 12 such as a filament, etc., are accelerated and converged by a high voltage of, for example, about 1 MV at the accelerating tube 13 and becomes a high speed electron beam. Then, to enlarge or reduce the beam diameter, the beam diameter is controlled by the focusing electromagnet 16 for converging to a beam of a constant diameter. In this construction, the focusing electromagnet 16 is an electromagnet which comprises a ring-shape coil which is placed around the main axis. By the focusing electromagnet, a magnetic field is formed symmetrically with respect to the axis in the direction of the beam axis, and the beam diameter is controlled in accordance with the magnitude and direction of the magnetic field. For the above purpose, a direct electric current I.sub.O, as shown in FIG. 3(b), is supplied to the electromagnet.
The electron beam, of which beam diameter is controlled by the focusing electromagnet 16, is scanned toward x and y directions by the scanning electromagnet 17. In this construction, the scanning electromagnet 17 is an electromagnet which comprises two sets of magnetic poles capable of deflecting an electron beam to x and y directions. By controlling the magnitude and direction of the electric current which is supplied to the coil of the electromagnet, the deflection angles in the x and y directions are controlled, the electron beam is scanned and the irradiated location of the electron beam is controlled. To this end, a sinusoidal AC current I.sub.S, as shown in FIG. 3(a), is supplied to the electromagnet coil. As a result, to the irradiation window 15, an electron beam is scanned in the left and right directions in FIG. 2(b) as shown therein. It should be noted that, in FIG. 2(a), the scan in the vertical direction is abbreviated for convenience of explanation.